The problem of venting is well known in the art. Indeed, it is well known that certain liquid substances generate gases and that this may lead to the build up of pressure inside a container containing such liquid substances. Such substances are typically hydrogen peroxide or other bleaches as well as carbonated beverages.
Should no precautions be taken to cope with this pressure build up, the container containing the substance may be subjected to severe stress which usually causes bulging or stress cracking. Bulging refers to the deformation of the container, while stress cracking may cause leakage or even bursting. Thus to avoid these phenomena, it is necessary to vent the container, i.e. to provide means whereby the pressure build up inside the container may be relieved. In other words, it is necessary to provide means whereby the gas generated by the liquid substance can escape to the ambient, while leaktightness of the container is maintained.
One means of achieving this is by providing a cap with a hole, and a membrane inserted in the cap, covering the hole. The membrane is permeable to gases but not to liquids.
There are a number of problems associated with the use of semi permeable membranes.
A first problem is that semi permeable membranes are expensive materials. It is therefore an object of the present invention to provide a venting cap which uses as little membrane material as possible. This object implies not only using small membranes, but also providing a process for manufacturing such a cap which drastically reduces the amount of wasted membrane material, i.e. the amount of membrane material not used for manufacturing caps. This process should of course be compatible with high production speeds required by modern industry.
In the art, it is customary to design membranes which are force fitted in the cap receiving the membranes. This is a fairly simple process because it requires no particular arrangement for securing the membrane to the cap. But in that configuration, it is essential that the membrane is as big as the inside dimensions of the cap, whereas this is not required from the standpoint of venting performance. Also, it implies that a new membrane design has to be developed for each and every cap. It is thus also an object of the present invention to provide a venting means which provides maximum flexibility in that it is applicable to a great variety of caps.
Another flexibility required is flexibility in the membrane material. Indeed, there are many different applications which require venting, and each of those different applications may require different membrane materials.
Yet another problem encountered with membranes is that they are typically made out of delicate items, both because of the materials typically used to make them, and because they are typically very thin. Thus they can very easily be damaged during the process of their insertion into the cap. It is thus another object of the present invention to obviate the need for special precautions during said insertion process.
In U.S. Pat. No. 4,765,499, an arrangement is proposed wherein a small membrane is fitted into a liner, the size of which corresponds to the inside diameter of the cap receiving the arrangement. This arrangement does not meet the objects of the present invention because it can only fit caps of a determined dimension, i.e. it does not provide the desired flexibility. Furthermore the arrangement in '499 cannot be obtained by a process meeting all of the above objects. Actually, '499 fails to disclose any suitable process at all.
In AU 9341259, a venting cap is disclosed wherein a small membrane is secured to the inner surface of the cap's top wall by ultrasonic welding. Because ultrasonic welding is an essential requirement for providing the arrangement, drastic limitations are imposed on suitable materials for that arrangement. i.e. one can only use materials which can be ultrasonically welded. The '259 arrangement thus does not provide the desired flexibility either.